Prevent implicit conversion of float to double to avoid precision
error on i686.

  https://github.com/Maratyszcza/FP16/issues/20

Taken from Debian:

  https://salsa.debian.org/deeplearning-team/fp16/-/blob/master/debian/patches/ftbfs-i386.patch

Index: fp16/include/fp16/fp16.h
===================================================================
--- fp16.orig/include/fp16/fp16.h
+++ fp16/include/fp16/fp16.h
@@ -228,7 +228,8 @@ static inline uint16_t fp16_ieee_from_fp
 	const float scale_to_inf = fp32_from_bits(UINT32_C(0x77800000));
 	const float scale_to_zero = fp32_from_bits(UINT32_C(0x08800000));
 #endif
-	float base = (fabsf(f) * scale_to_inf) * scale_to_zero;
+	const volatile float base_inf = fabsf(f) * scale_to_inf;
+	float base = base_inf * scale_to_zero;
 
 	const uint32_t w = fp32_to_bits(f);
 	const uint32_t shl1_w = w + w;